Screen Redraws (Surface Redraws, GPU Redraws) in Wayland

[Daniel Stone]

Hi Ryan,

On 12 May 2017 at 17:10, Ryan Sipes <ryan at system76.com> wrote:

> New to Wayland and had a big question. I was curious as to whether work
> had gone into when screen redraws were made (they are called "Surface
> Redraws" and "GPU Redraws" in Android). I know in Android this has resulted
> in better battery life. I'm sure many in this mailing list know, but what
> it does is only redraws when changes have been made. Is this on the
> roadmap? Has it already been implemented? I know it was on the roadmap for
> Mir, so I'm curious if it is an consideration in Wayland.
>
> Love the work, using Wayland right now with multiple monitors and it works
> great!
>

Depends what you mean by 'Wayland', I guess! But most servers (Weston,
Mutter/GNOME, KWin, Enlightenment) certainly do this. Repaints only happen
once per screen refresh cycle (vsync), and also only when client content
has changed and requires an update. This timing information is also passed
down to clients, who latch on to the clock to themselves only issue redraws
once per frame: the 'frame clock' setup was one of the bigger and more
invasive changes in GTK+3, but means those (also Qt, Clutter, GL and I
think also EFL) clients don't repaint unnecessarily.

You can find some more on Pekka's blog - it's fairly old, but still goes
into some of the details:
http://ppaalanen.blogspot.co.uk/2015/02/weston-repaint-scheduling.html

Cheers,
Daniel
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